One new update in Lubuntu 15.04 that hasn't got much attention is there was an update in lxrandr to 0.3.0 Has improved multiple montior support with quick options to allow you to show different screens either above or to the right of the primary monitor or a simple checkbox to for example select only show external monitor if you plug laptop into a new monitor with a much higher resolution, for example , 1920x1080 than a 1366x768 screen built into my aging over 5 year old laptop. For previous or even more complicated setups previously I had used the heavier resource wise arandr which is a quite nice application for setting up dual screen displays but written in python2 and gtk2. I remember being at ubucon at scale in 2014 and tihnking hmm it would be easier if the presenter was using arandr to setup the multiple monitor setup. Although even among people that love arandr if you install it there is also an unxrandr command that gives your current screen configuration and outputs how to recreate it with xrandr which If you bind it to a key for a multiple monitor setup could be conbient. This function needs the functionality of arandr and cannot easily be released as a standalone program.
This makes it a lot easier to set up mulitple monitors or even have just use the external one if it is much bigger and multiple monitors of different sizes doesn't appeal to you.http://brendanperrine.com/screenshotgal/quickoptions.png
This is a view of a simple screenshot of this new interface. Although the manual test for lxrandr never got updated I think I started on work on that but never finished.